This application is a national phase of PCT/FR00/03612 filed Dec. 20, 2000, claiming priority of French Appln. No. FR 99 16241, filed Dec. 22, 1999, all of which are included in their entirety by reference made hereto.
1. Field of the Invention
The present invention relates to an Eddy current retarder for a vehicle, intended to slow the rotation of a shaft driven about its axis.
Among such retarders, the invention relates more especially to those which are intended to slow the rotation of an engine shaft driven about its axis, particularly the crankshaft of a vehicle engine, this engine having a casing which itself comprises a frontal wall stretching substantially in a plane perpendicular to the axis of the crankshaft, which crankshaft has one end which is directed toward the frontal wall of the casing of the engine and in the region of which the retarder is mounted overhangingly on the frontal wall of the casing of the engine via connecting means, the retarder comprising a rotor part which rotates as one coaxially with the crankshaft, a stator part coaxial with the crankshaft and secured to the frontal wall of the casing of the engine, an armature belonging to the rotor part and an inductor belonging to the stator part, the inductor being arranged on a stationary annular component of the stator part, facing the armature.
2. Description of the Prior Art
Document JP9201037 describes an Eddy current retarder of the abovementioned type.
Such a retarder has the advantage of having a simplified structure and a low weight and size, given its geometry with a ferromagnetic central disk rotating as one with the crankshaft and rotating between two disks which support energizing means consisting of permanent magnets projecting axially toward the central disk, it being possible also for one of the two disks with permanent magnets to be rotated by a servomotor.
However, the main disadvantage with this retarder is that its braking torque is difficult to control. This is because two disks are equipped with permanent magnets, the magnetic flux of which is difficult to control. In particular, this retarder does not make it possible to completely cancel the magnetic flux, particularly the magnetic flux tangential to the disks, which remains very high.
Another disadvantage of this retarder lies in the fact that it is arranged between the engine and a pulley that drives the timing and accessories, said pulley being situated at the output of the crankshaft. What this means is that the pulley, thus distanced from the engine, will give rise to a significant overhang of the belt that drives the engine auxiliaries, which belt habitually runs around this pulley, such an overhang entailing moving all the accessories, and therefore creating a similar overhang in said auxiliaries in order to avoid, in the long term, causing this belt running around the pulley to break.
A particular object of the present invention is to overcome these drawbacks.
To this end, the rotor part of the retarder according to the invention has symmetry of revolution about the axis of the crankshaft so that it has a peripheral face facing a peripheral face of the stator part, the inductor of the retarder having at least one electromagnetic winding.
Thus, the Eddy current retarder maintains a compact structure while at the same time allowing simple and easy control over its magnetic flux by virtue of the presence of electromagnets.
In some preferred embodiments of the invention, recourse is had to one and/or other of the following arrangements:
the rotor part has an external component of substantially cylindrical shape which surrounds the stator part and which constitutes the armature of the retarder, said external component having a radial flange secured to the crankshaft, said flange being pierced with a number of holes;
the inductor of the retarder is an inductor with poles each surrounded by an induction winding and projecting radially outward on the external face of said annular component of the stator part;
the poles are secured to a first annulus, while the collection of induction windings constitutes a second annulus of larger diameter than that of the first annulus, said second annulus being assembled coaxially with said first annulus by fitting each pole into a respective induction winding;
the inductor of the retarder is an inductor with claws and with one single induction winding;
a first set of claws constitutes a first annulus and a second set of claws constitutes a second annulus with the same diameter as that of the first annulus, said induction winding surrounding a cylindrical component of a diameter smaller than that of the first and second annuli, these being assembled coaxially with said cylindrical component in such a way that each claw of the first set of claws is interspersed between two adjacent claws of the second set of claws;
the connecting means comprise a framework which has at least one substantially radial flange centered on the crankshaft and pierced with a number of holes, said flange itself having arms which extend from it toward the engine to secure the framework to the frontal wall of the casing of the engine, the electromagnetic retarder being housed in a space delimited by the flange, the fixing arms and the frontal wall of the engine;
a pulley situated at the output of the crankshaft is arranged between the casing of the engine and the retarder; the flange of the external component advantageously incorporating the pulley, so as to reduce the number of parts in the assembly;
said induction winding (or windings) is (or are) energized from an electrical source, which is regulated for power, of the vehicle.